linux-kernel - Re: [RFC PATCH v5 038/104] KVM: x86/mmu: Allow per-VM override of the TDP max page level

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Date:   Fri, 01 Apr 2022 18:15:34 +1300
From:   Kai Huang <kai.huang@...el.com>
To:     isaku.yamahata@...el.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     isaku.yamahata@...il.com, Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>, erdemaktas@...gle.com,
        Connor Kuehl <ckuehl@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC PATCH v5 038/104] KVM: x86/mmu: Allow per-VM override of
 the TDP max page level

On Fri, 2022-03-04 at 11:48 -0800, isaku.yamahata@...el.com wrote:
> From: Sean Christopherson <sean.j.christopherson@...el.com>
> 
> In the existing x86 KVM MMU code, there is already max_level member in
> struct kvm_page_fault with KVM_MAX_HUGEPAGE_LEVEL initial value.  The KVM
> page fault handler denies page size larger than max_level.
> 
> Add per-VM member to indicate the allowed maximum page size with
> KVM_MAX_HUGEPAGE_LEVEL as default value and initialize max_level in struct
> kvm_page_fault with it.
> 
> For the guest TD, the set per-VM value for allows maximum page size to 4K
> page size.  Then only allowed page size is 4K.  It means large page is
> disabled.

Do not support large page for TD is the reason that you want this change, but
not the result.  Please refine a little bit.

> 
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---
>  arch/x86/include/asm/kvm_host.h | 1 +
>  arch/x86/kvm/mmu.h              | 2 +-
>  arch/x86/kvm/mmu/mmu.c          | 2 ++
>  3 files changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index d8b78d6abc10..d33d79f2af2d 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1053,6 +1053,7 @@ struct kvm_arch {
>  	unsigned long n_requested_mmu_pages;
>  	unsigned long n_max_mmu_pages;
>  	unsigned int indirect_shadow_pages;
> +	int tdp_max_page_level;
>  	u8 mmu_valid_gen;
>  	struct hlist_head mmu_page_hash[KVM_NUM_MMU_PAGES];
>  	struct list_head active_mmu_pages;
> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> index 0ae91b8b25df..650989c37f2e 100644
> --- a/arch/x86/kvm/mmu.h
> +++ b/arch/x86/kvm/mmu.h
> @@ -192,7 +192,7 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
>  		.is_tdp = likely(vcpu->arch.mmu->page_fault == kvm_tdp_page_fault),
>  		.nx_huge_page_workaround_enabled = is_nx_huge_page_enabled(),
>  
> -		.max_level = KVM_MAX_HUGEPAGE_LEVEL,
> +		.max_level = vcpu->kvm->arch.tdp_max_page_level,
>  		.req_level = PG_LEVEL_4K,
>  		.goal_level = PG_LEVEL_4K,
>  	};
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index a474f2e76d78..e9212394a530 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -5782,6 +5782,8 @@ void kvm_mmu_init_vm(struct kvm *kvm)
>  	node->track_write = kvm_mmu_pte_write;
>  	node->track_flush_slot = kvm_mmu_invalidate_zap_pages_in_memslot;
>  	kvm_page_track_register_notifier(kvm, node);
> +
> +	kvm->arch.tdp_max_page_level = KVM_MAX_HUGEPAGE_LEVEL;
>  }
>  
>  void kvm_mmu_uninit_vm(struct kvm *kvm)